In November 2008, at the height of the global downturn, the Queen had asked academics at the London School of Economics: "Why did nobody notice it?" and described the crisis as "awful".

But on Thursday, on a visit to the Bank of England with the Duke of Edinburgh, she got a thorough answer from Sujit Kapadia from the Bank's Financial Services Committee.

Mr Kapadia gave the Queen three reasons why it happened. He told her that financial crises were like earthquakes and flu pandemics and, because they are rare events, they are difficult to predict. He also said there was a new paradigm where people thought that markets were efficient and risks could be managed better than before.

"People thought markets were efficient, people thought regulation wasn't necessary," he told the Queen. "Because the economy was stable there was this growing complacency. (Thirdly) people didn't realise just how interconnected the system had become."

The Queen appeared quite interested in the discussion, asking what authorities were doing now to prevent another global downturn. She remarked to workers: "People got a bit lax... perhaps it is difficult to foresee (a financial crisis)."

When told by an employee that the men and women in the room were there to prevent another one, the Duke jokingly said: "Is there another one coming?"

Mr Kapadia said the Queen was very interested in what the Bank was trying to do to prevent another crisis.

The Queen and the Duke also toured vaults full of thousands of slabs of gold worth billions of dollars and briefly inspected some of the gold.

The royal couple then signed a million pound note each for the Bank's guest book.